Process of recovering acetic acid in producer-gas plants.



SNVENTOR$ Patented July 18,1911.

3 2 MEETS-SHEET 1.

W. J. GROSSLEY & T. RIGBY.

PROCESS or REGOVERING AGETIG ACID IN PRODUCER GAS PLANTS.

APPLICATION FILED AUG. 17, 1909.

m 1 #21 r x 1 1W (x I m QJ y K J IMHHI H l l h 1 1 1 H m N INK! R f C W. J. GROSSLEY & T. RIGBY. PROCESS OF BEGOVEBING AOETIO ACID IN PiidDUOEB GAS PLAN 1Y8, APPLIOATIOI IILBD AUG. 17, 1909.

998,234 Patented July-18; 1-911.

1 a sums-31mm 2.

. WITNE55 INVENTORS' ww wa fication.

' ments in. the recovery UNITED STATES rA rnN OFFICE.

wILLtAm JGEN onossLnY AND rnomes many, or MANCHESTER, ENGLAND.

rrtocass or RECOVERING 'acnrrc horn IN rnonucnreens rLAN'rs.

Application filed August 17, 1909. Serial No. 513,806.

Yb all whom it may concern:

Be 'it known that We, WILLIAM JOHN? GnossLnr and THoMAs RIGBY, both subjects of the King of Great Britain, residing the former at Openshaw, Manchester, in the} county of Lancaster, England, and the latl ter at 948 Ashton Old Road, Fairfield, Man; chester aforesaid, have invented new and useful Improvements in the Process of Recovering Acetic Acid in Producer-Gas Plants, of which the following is a specii at low temperatures, and in consequence a considerable proportion of the original ni-. trogen contained in the fuel is recovered in the form of ammonia. In order' to make such a -process an economic success it is found necessary in practice to cool the gases leaving he gas producer to such a temperature that great proportion of the sensible t) at of the gases and the sensible and latent {heat of the steam present in the gases is reficovered. A portion of the sensible heat is rbcovered by superhating the air and steam on their Way to the gas producers. To recover the greater portion of the remainder of the heat it is usual to cool the gases and condense the water vapor present in them by means of circulating water or liquor, which heat isafterward recovered by regeneration in an air saturating tower.

' In the accompanying 2 sheets of drawings, *igure 1 is a diagram of what is com-- monly known as the Mond type of plant. Fig. 2 a diagram of the Crossley and Rigby type of plant, fitted .with apparatus for recovering acetic acid and the vapors of evaporation hereafter described.

For the better understanding of our intower D use if intended for heatin vention We will briefly describe the existing types of plant.

In Fig. 1 it will'be seen that the gases produced in the-gas producer A, are passed through the superheater B before entrance in-to'the mechanical Washer C. In the mechanical-washer C they are cooled by water Specification of Letters Patent. 'Patented July 18, 1911.

spray and freed from the dust they usually I contain, leaving the washer at a temperature approximately ninety degrees centigrade.-

The gases are then passed through an-acid where ascending through checker work they are met by a stream of sulfate which is to cool them to a still lower tem-.

nerature and condense most of the Water liquor containing free sulfuric acid in# its composition torabsorb the ammoniapresent 'in' the gases.

vapor present-in them. This is effected by water which is pumped up and circulated down the tower F through checker work and in the opposite direction to the gases ascending'through the checker work. Leaving the gas cooling tower they are usually taken away through a pipe X directly for subjected to further cooling and purificar tion if they are to be used in gas engines; The water leaving the foot'of the gas cooling tower F in a heated condition passes into the tank G from whence it is'pumped' by the pump H to the top of the third tower J known as the'air saturating tower, where, descending through checker work it is met by air from the blower K on its way to the g purposes, or are gas producers and the intimate contact obtained causes the water to be cooled and the air to be heated and fully saturated with water vapor at the temperature ltilQflVt-BS the tower. The saturated air is then passed by way of the pipeM to the superheaters and gas producers, while the water leaving the foot of the tower J passes into the tank-N and is re-circulated by means of the pump P through the gas cooling tower F. These interchanges of heat take place continuously.

with

An improved system was brought out by the present applicants and British Letters Patent numbered 24.14% of 1906 were grant ed to them, for such system, which mainly consists in washing and cooling the gases, condensing the water vapor and absorbing the ammonia in one and the same apparatus. In addition to this the actual. sulfate liquor circulated is used for the purpose of simultaneously saturating the air with water va per in the air saturating tower and simultaneously this action cools the liquor suiticiently for it to be used for re-circulation through the washing, condensing and absorbing apparatus. By this means a considerable reduction in the number of parts is made. in such recovery plants when using certain fuels, such as peat, considerable quantities of acetic acid are given off with the gases and the object of this invention is to provide means for successfully'recovcring this acetic acid in marketable form, without prejudicing the yield of ammonia. In practice acetic acid, although having a higher boiling point than water, is very volatile and is somewhat difiicult to recover at any temperature.

i fhen gasifyi'ng peat in the Mond type of plant a portion of the acetic acid is condensetl and brought down in the mechanical gas washer in solution with the water contained therein, either as acetic acid or incombination. A large proportion of acetic acid is also condensed and recovered in the next apparatus, namely the acid tower and a further large proportion is recovered in the water circulated through the gas cooling tower. /Vhen using the Mond type of plant we systematically take the water from the mechanical gas washer and add it to the sulfate liquor which is being circulated through the acid tower, and as a result any acetate of ammonia contained therein is broken up and the ammonia absorbed by the sulfuric acid, thereby forming sulfate of ammonia and leaving the acetic acid in solution in the liquor. We find when using our aforesaid patented system that most of the acetic acid is recovered in the sulfate liquor and this 15 peculiarly desirable when using the process hereinafter described.

it is usual with both the aforesaid typesof plant to keep the sulfate liquor in circulation a strength of from thirty to forty degrees Twaddell, afterward concentratingit further in evaporating pans for the purpose of crystallization of the sulfate in the marketable form, the mother liquor drained from the crystals being passed again into the sulfate liquor for circulation. Vl hilc this evaporation is taking place in the pans we L'ind that most of the acetic acid contained in the sulfate liquor is passed oil with the 'method is abnormally large.

vapors of evaporation. These vapors of evaporation are usually Wasted but in this invention we treat them in such a manner that the acetic acid is recovered and this re covery of the acetic acid from the vapors of evaporation may be done in any suitable and known manner and We deliberately arrange the process of recovery .so that all or most of theacetic acid is contained in the sulfate liquor. We find that it is an easy matter to pass over ninety per cent. of the acetic acid contained in the liquor away with the apors of evaporation, even though the temperature of evaporation be lower than the boiling temperature of pure acetic acid, and that portion of the acetic acid which is not passed over with the vapors remains in the mother liquor drained from the crystals, and being re-circulated with the sulfate liquor, practically all of it is finally recovered. o wish to make it quite clear that we do not limit our claims to any particular form of recovery of the acetic acid from these vapors of evaporation, but claim broadly the process of collecting the acetic acid in the sulfate liquor and recovering the acetic acid in any desirable manner from the vapors of evaporation given oil during concentration of the'sulfate liquor.

One of the methods in which the acetic acid may be recovered from the vapors of evaporation is to pass thesev vapors through a surface condenser or equivalent arrangemcnt in such a manner that the vapors are condensed, so forming a dilute solution of acetic acid. If this method is adopted a still or like apparatus becomes necessary to recover the acetic acid in marketable form. Another method is to condense the vapors by direct contact with water or any suitable liquor in such a manner that the acetic acid is condensed with the steam and taken up in solution with the condensing liquor but the quantity of liquor to be treated by this The method which we find most practicable and which we prefer to use is as is hereinafter described, wherein the acid. vapors are arranged to saturate air or other suitable gases intended for the'gas producer before being washed by a suitable alkaline solution. No stills or other apparatus necessitating auxiliary heatare required by this method and the same concentration of the liquor which is neces sary to make ammonium sulfate crystals also enables the acetic acid to be recovered con tinuously.

We have previously stated that the acetic acid is very volatile at all temperatures up to its boiling point and We find this to be the case whether 'it is in solution with Water or sulfate liquor, and as a consequence when circulating with sulfate liquor or water in ratus betweenthe air saturating tower and the superheaters and gas producers and in such an arrangement we wash the saturated air from the air saturating tower with a hot .alkaline solution, such as milk of lime or soda, intimate contact being obtained with the saturated air in anysuitable manner.

In Fig. 2 it' will be seen that an alkaline washer a is'used forthe purpose of recovering the acids contained not only in the air supplied through the pipe I) from the air saturating tower, b to the air main (Z, but also that contained in the vapors of evaporation from the evaporating pan 0 and this is done by passing the vapors of evaporation through the pipe 0 into the air main d, conveying the saturated air from the air saturating tower b, the mixture being Washed by a .heatedalkaline solution in one and the same apparatus a. 'It'is obviously desirable to arrange this combination where possible I and We prefer generally touse an appara-' tus of this nature when recovery of the acetic acid is' carried out. The alkaline solution in the washer a is kept heated by any suitable means but we prefer toarrange that the alkaline liquor be circulated in contactwith the hot gascoming from the super:- heaters e and before entrance to theammonia absorbing apparatus g. The liquor is shown in Fig. 2 circulated by means of the pump 72/ through the pipe h to the liquor heating device 7', the heated liquor leaving the device 7' being conveyed back to the Washer a by means of the'pipe 70. It will also be seen that the air leaves the washer a by means of the pipe on being thence conveyed direct to the superheater e and so on through the air supply pipe m to the gas Y producer n. From the producer n the hot gases pass through the superheater e and pipe a through the liquor heating device 7' to the ammonia absorber g the purified gases leaving the absorber by a pipe 9' whence they are conducted to any point desired. From the absorber g the acid liquor overflows into a tank w whencit is pumped by a pump 'w'through a pipe. Q02 to the air saturating tower I). From the tower b the acid liquor returns through the settling tank 2 to the-ammonia absorber g. The alkaline solution in the Washer a is usuallyheated at or above the temperature of saturation in. such an arrangement so that condensation of vapor in the pipe mis reduced to a minimum. Besides recovering the acetic acid we also recover the heat of the vapors of evaporation and we find that the air supplied t-hrough-the pipes m, m, to the gas producers instead of being saturated at about seventy three degrees centigrade as is usual from an air saturating tower such as b, is now saturated at nearly eighty degrees centigrade,,without addition of any auxiliary steam. The acetate formed in the washer a'contains in practice small quantities of impurities but there is no difficulty in obtaining an acetate of a strength sufficient for commercial purposes. The alkaline liquor is taken away fromthe washer a from time to time and treated linthe usual manner for recovery of the acetate in marketable form.

,Larg'e quantities of steam have to be used in all cases with the air blast maintained by the blower K to keep the producers n at a low temperature, and in practice most of this steam has to be raised from auxiliary sources. By utilizing these acid vapors after neutralization a considerable quantity of otherwise wasted heat is recovered and the size of the auxiliary steam raising plant can be correspondingly reduced While at the same'time the acetic acid is recovered in marketable form.

When we mention in this specification, a washer or scrubber, which we wish to 'use in our processes, We wish it to be understood that we do not limit our claims to the forms of Washer or scrubber shown in the drawings but may use any known apparatus designed with a similar object for the same purpose. We also Wish it to be understood that our descriptions of the Mond system and Crossley and Rigby system are as they are commonly used, but that variations are made with both types of plant. in the. form of apparatus although the same principles involved are generally applied.

What we claim as our invention and desire to secure by Letters Patent is l.'The process of recovering'acetic acid from the gases given off by fuel in recovery plants, which consists in subjecting the gases to the action of a sulfateliquor containing free sulfuric acid, concentrating the result-' ing liquid, saturating gases with thevapors tration, Washing said saturated gases with a liquid and recovering the acetic acid from said last-mentioned liquid.

2. The process of recovering acetic acid from the gases given off by fuel in recovery plants, Which consists in subjecting the gases to the action of a sulfate liquor containing free sulfuric acid, concentrating the resulting liquid, saturating gases with the vapors of evaporation given ofl during said concentratlon, washing said saturated gases with an alkaline solution and recovering the acetic acid from said solution.

of evaporation given off during said concen- 3. The process of recovering acetic acid from the given off by fuel in recovery plants which consists in subjecting the gases the act in of a sulfate liquor containing ncicl, csncentratin the resultliq u saturating gasesqvit the vapors oit' evspomtion tn 0% during said concen- 'tlfLtlOll, "slung said saturated gases With a ed alkaline solution and recovering the nee-tic said from saicl solution.

In testimony whereuf We have signed our names to this specification in the presence of two subscribing Witnesses.

WILLIAM JOHN GROSSLEY. THOMAS RIGBY. Witnesses to signatureof William John Crossley:

DAVID CORRY, RICHARD JAMES. Witnesses to signature of Thomas Rigby:

JOSEPH CARTER, ALBERT OGDEN. 

